1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an array substrate of the LCD device having thin film transistors.
2. Description of Related Art
In general, a liquid crystal display (LCD) device displays an image using a plurality of pixels. The LCD device having a thin film transistor (TFT) as a switching element is typically called a thin film transistor liquid crystal display (TFT-LCD) device.
A typical liquid crystal display device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite orientational order in arrangement resulting from their thin and long shapes. The arrangement direction of the liquid crystal molecules can be controlled by supplying an electric field to the liquid crystal molecules. In other words, if electric fields are applied to the liquid crystal molecules, the arrangement of the liquid crystal molecules changes. Since incident light is refracted according to the arrangement direction of the liquid crystal molecules due to the optical anisotropy of the arranged liquid crystal molecules, image data can be displayed.
By now, an active matrix LCD (AM-LCD) that the thin film transistors and the pixel electrodes are arranged in the form of a matrix is receiving a great deal of attention due to its high resolution and superiority in displaying moving video data.
FIG. 1 is a cross-sectional view illustrating a conventional liquid crystal display (LCD) panel. As shown in FIG. 1, the LCD panel 20 has lower and upper substrates 2 and 4 with a liquid crystal layer 10 interposed between the lower and upper substrates 2 and 4. The lower substrate 2 has the TFT xe2x80x9cSxe2x80x9d as a switching element to change an orientation of the LC molecules and includes a pixel electrode 14 to apply a voltage to the LC layer 10 according to signals of the TFT xe2x80x9cSxe2x80x9d. The upper substrate 4 has a color filter 8 for implementing colors and a common electrode 12 on the color filter 8. The common electrode 12 serves as an electrode for applying a voltage to the LC layer 10. The pixel electrode 14 is arranged over a pixel portion xe2x80x9cPxe2x80x9d, i.e., a display area. Further, to prevent leakage of the LC injected into a space between the two substrates 2 and 4, the two substrates 2 and 4 are sealed by a sealant 6.
FIG. 2 is a plan view illustrating an array substrate. A gate line 22 is arranged in a transverse direction and a data line 24 is arranged in a longitudinal direction perpendicular to the gate line 22 such that pixel region having pixel electrode 14 is defined by the gate line 22 and the data line 24.
In the AM-LCD, the switching element (TFT xe2x80x9cSxe2x80x9d) applying the voltage to the LC layer 10 (see FIG. 1) is formed nearby the cross point of the gate line 22 and the data line 24. The TFT xe2x80x9cSxe2x80x9d has a gate electrode 26 extended from the gate line 22, a source electrode 28 extended from the data line 24 and a drain electrode 30 electrically contacting the pixel electrode 14 via contact hole (not shown). When the gate electrode 26 of the TFT receives gate signals, in the ON-state, the data line 24 transmits data signals to the pixel electrode 14. On the other hand, when the gate electrode 26 is in the OFF-state, data signals are not transmitted to the pixel electrode 14. In general, a manufacturing process depends on the materials of the elements used, and on the intended design. For example, the resistivity of the material used in the gate line and the data line determines the picture quality in a large LCD panel (over 18 inches) and in an LCD panel having a high resolution. In the case of these LCD panels, the material such as Aluminum (Al) or Al-alloy is used for the gate line and data line.
FIGS. 3a to 3d are cross-sectional views illustrating process steps for fabricating a conventional array substrate for the active matrix LCD device.
An inverted staggered type TFT is generally used for an LCD device due to the simple structure and superior efficiency. The inverted staggered type TFT includes a back channel etched type (EB) and an etch stopper type (ES). The manufacturing method of the back channel etched type TFT will be explained hereinafter.
First, a first metal layer is deposited on a substrate 1 by a sputtering process after a cleaning process which enhances adhesion between the substrate 1 and a metal layer and removes organic materials and alien substances from the substrate. FIG. 3a shows a step for forming the gate line 22, the gate electrode 26 and a capacitor electrode 32 by patterning the first metal layer using a first mask. As a metal for the gate electrode 26, Aluminum is mainly used so as to reduce the RC delay owing to its low resistance. However, pure Aluminum is weak in acidity and may result in line defects by a formation of a hillock during a high temperature process, so Aluminum alloy and multi-layered Aluminum are used.
Referring to FIG. 3b, the gate insulation layer 34 is formed on the entire surface of the substrate 1, while covering the gate line 22 and the gate and capacitor electrodes 26 and 32. Then, a pure amorphous silicon (a-Si:H) layer and a doped amorphous silicon (n+a-Si:H) layer are formed in series on the gate insulation layer 34. As shown in FIG. 3b, an active layer 36 and an ohmic contact layer 38 are formed by patterning the silicon layers. The ohmic contact layer 38 reduces contact resistance between the active layer 36 and an electrode that will be formed later.
As depicted in FIG. 3c, the data line 24 and the source and drain electrodes 42 and 44 are formed by depositing, and then patterning, a second metal layer. A metal for the source and drain electrodes 42 and 44 may be selected from Cr, Mo, or the like. The portion of the ohmic contact layer 38 on the active layer 36 is etched using the source and drain electrodes 42 and 44 as a mask. If the ohmic contact layer 38 between the source and drain electrodes 42 and 44 is not removed, serious problems such as deterioration of electrical characteristics and efficiencies can be caused in the TFT xe2x80x9cSxe2x80x9d (see FIG. 2). Etching the portion of the ohmic contact layer 38 over the gate electrode 26 requires special attention. While etching the ohmic contact layer 38, the active layer 36 is over-etched by 50-100 nm due to the fact that the active layer 36 and the ohmic contact layer 38 have the same etch selectivity. This is because etching uniformity directly affects the electrical characteristics of the TFT.
As shown in FIG. 3d, a protection layer 46 is formed on the source and drain electrodes 42 and 44 in order to protect the active layer 36 by depositing, and then patterning, an insulating material. Due to an unstable energy state of the active layer 36 and an alien substances generated during the etching process (which affect electrical characteristics of the TFT), the protection layer 46 is usually made of a material selected from inorganic materials such as SiNx and SiO2, or organic materials such as BCB (benzocyclobutene). In addition, the protection layer 46 is used as a material having high light transmittance, humidity resistance and durability, in order to protect the channel area of the TFT and major portions of a pixel region from possible humidity and scratch (occurring during later process steps).
A contact hole 45 is formed in the protection layer 46 to expose the portion of the rain electrode 44. FIG. 3d also shows a step of forming a pixel electrode 40 by depositing, and then patterning, a transparent conducting oxide (TCO) layer. Indium tin oxide (ITO) is usually employed for the transparent conducting oxide layer. The pixel electrode 40 makes electrical contact with the drain electrode 44 via the contact hole 45 and overlaps the capacitor electrode 32 to form a storage capacitor.
In the above-mentioned process, the gate insulation layer 34 is formed to insulate the gate electrode 26 from the active layer 36, generally by using a Chemical Vapor Deposition (CVD). However, while forming the gate insulation layer 34 using the CVD equipment, various kinds of gases are used therein. Then alien substances or defects can be formed in the decomposition process of these gases.
FIG. 4 is an enlarged view of the portion xe2x80x9cHxe2x80x9d of FIG. 3d, which is the same as the portion xe2x80x9cHxe2x80x9d of FIG. 2. The portion xe2x80x9cHxe2x80x9d is the cross point of the gate line 22 and the data line 24. As shown in FIG. 4, the gate insulation layer 34 is formed between the gate and data lines 22 and 24. When forming the gate insulation layer 34 on the gate line 22, the alien substance xe2x80x9cPxe2x80x9d can be deposited from the CVD equipment. If the alien substance xe2x80x9cPxe2x80x9d is deposited on the gate line 22 in the portion xe2x80x9cHxe2x80x9d where the gate and data lines 22 and 24 cross each other, unusual growth occurs in the portion xe2x80x9cHxe2x80x9d during the process of forming the gate insulation layer 34. When the data line 24 is formed on the unusual-growing gate insulation layer 34, a short circuit occurs between the gate and data lines 22 and 24. The alien substance, and related defect, have caused serious problems in the conventional art due to the impossibility of repair. Therefore, the gate and data lines 22 and 24 acquire a line defect causing serious inferiority in the LCD device.
FIG. 5 is a cross-sectional view taken along line Vxe2x80x94V of FIG. 2 illustrating the cross point of the gate and data lines 22 and 24. The data line 24 on the gate insulation layer 34 can be open, owing to the step portion of the gate line 22. Therefore, this also is a line defect, and causes decreased manufacturing yields of the LCD device.
An object of the present invention is to provide a TFT array substrate for use in an LCD device, and more particularly, an array substrate having a repair structure when a short occurs between gate and data lines or when the data line is open.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a TFT array substrate for use in a liquid crystal display device, including: a substrate; a gate line formed on the substrate, arranged in a transverse direction and having a gate electrode; a data line insulated against the gate line by a first insulation layer, arranged in a longitudinal direction perpendicular to the gate line, the data line having a source electrode near the cross point of the gate and data lines and having first and second data lines which are defined separately by the cross point of the gate and data lines; a drain electrode spaced apart from the source electrode over the gate electrode; a first repair line extended from the first data line and crossing the gate line; a pixel electrode connecting to the drain electrode; and a second repair line insulated against the data line by a second insulation layer, and overlapping the second data line and a free end of the first repair line.
The second repair line of the TFT array substrate is made of the same material as the pixel electrode.
In order to achieve the above objects, in another aspect, the preferred embodiment of the present invention provides a TFT array substrate, including: a substrate; a gate line formed on the substrate and arranged in a transverse direction; a data line insulated against the gate line by a first insulation layer and arranged in a longitudinal direction perpendicular to the gate line; the gate line having first and second gate lines which are defined separately by the cross point of the gate and data lines; the data line having third and fourth data lines which are defined separately by the cross point of the gate and data lines; a thin film transistor having gate, source and drain electrodes; a pixel electrode connecting to the drain electrode of the thin film transistor; and a repair line insulated from the gate and data lines by a second insulation layer, and overlapping the first and second gate lines and the third and fourth data lines.
The repair line of the second embodiment of the present invention is made of the same material as the pixel electrode. Further, the repair line crosses the gate line at the cross point of the gate and data lines.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
In the drawings:
FIG. 1 is a cross-sectional view illustrating a general liquid crystal display (LCD) panel;
FIG. 2 is a plan view illustrating a pixel of the conventional LCD panel;
FIGS. 3a to 3d are cross-sectional view taken line IIIxe2x80x94III of FIG. 2 and illustrates process steps of fabricating a conventional TFT array substrate;
FIG. 4 is an enlarged view of the portion xe2x80x9cHxe2x80x9d of FIG. 3d; 
FIG. 5 is a cross-sectional view taken line Vxe2x80x94V of FIG. 2;
FIG. 6 is a plan view illustrating a pixel of the embodiment of the present invention;
FIG. 7 is a cross-sectional view taken line VIIxe2x80x94VII of FIG. 6;
FIG. 8 is a cross-sectional view taken line VIIIxe2x80x94VIII of FIG. 6;
FIG. 9 is a similar view to FIG. 8 and illustrates a method of repairing the short of the gate and data lines according to a first embodiment of the present invention;
FIGS. 10a to 10c are plan views illustrating repair structures according to a second embodiment of the present invention.